JP5310961B2 - High carbon steel wire rod with excellent drawability and fatigue properties after drawing - Google Patents

Abstract

High performance high carbon wire with refined inclusions after wire rolling, extremely low wire breakage rates at the time of drawing even in tough applications, and excellent in fatigue characteristics after wire drawing, characterized by having a predetermined composition of ingredients and in that the number ratio of inclusions satisfying (% SiO2)=40 to 95%, (% CaO)=0.5 to 30%, (% Al2O3)=0.5 to 30%, (% MgO)=0.5 to 20%, and (% MnO)=0.5 to 10% and further satisfying (% Na)=0.2 to 7% and (% F)=0.17 to 8% (below, referred to as "inclusions covered due to composition") in the oxide-based nonmetallic inclusions of a short axis of 0.5 mum or more, a long axis of 1.0 mum or more, and a circle equivalent diameter (area converted to diameter) of 1 mum or more which are seen in the L direction cross-section of the wire (below, referred to as "inclusions covered due to size"), that is, the number of inclusions covered due to composition/number of inclusions covered due to size×100, is 80% or more.

Description

  TECHNICAL FIELD The present invention relates to a high carbon steel wire and a valve spring wire excellent in wire drawing and fatigue resistance after wire drawing.

  The wire rod of the present invention is used, for example, for steel cords for automobile tires, saw wires for cutting silicon solar cells or semiconductors, automobile engine valve springs, long rubber belts, various wires for aircraft, ropes for bridges, etc. after wire drawing. .

  Generally, a high carbon steel wire used for wire drawing needs to be capable of high-speed wire drawing and excellent in fatigue resistance after wire drawing. One factor that adversely affects these properties is a hard oxide-based nonmetallic inclusion.

Among oxide inclusions, single composition inclusions such as Al ₂ O ₃ , SiO ₂ , CaO, TiO ₂ and MgO, or binary MgO · Al ₂ O ₃ and 2MgO · SiO ₂ have hardness. High and non-viscous. Therefore, in order to produce a high carbon steel wire excellent in drawability, it is necessary to increase the cleanliness of the molten steel and soften the oxide inclusions.

Thus, as a method for increasing the cleanliness of steel and softening non-metallic inclusions, Patent Document 1 discloses a method for producing steel for high carbon steel with good drawability. Patent Document 2 discloses a method for manufacturing an extra fine wire. The basic idea of these techniques is limited to ternary oxide-based non-metallic inclusions of Al ₂ O ₃ —SiO ₂ —MnO.

Patent Document 3 proposes to improve the drawability of the product by making the non-metallic inclusions a spesatite region in a ternary phase diagram of Al ₂ O ₃ , SiO ₂ , and MnO. Patent Document 4 discloses a method of reducing the harmful inclusions and improving the drawability by regulating the amount of Al added to the molten steel.

  In Patent Document 5, regarding the production of a steel cord having an inviscid inclusion index of 20 or less, pre-deoxidation was performed by blowing a CaO-containing flux together with a carrier gas (inert gas) into a ladle molten steel under Al complete regulation. Later, it has been proposed to soften inclusions by blowing an alloy containing one or more of Ca, Mg, and REM.

  Among the above methods, the method of modifying the ternary nonmetallic inclusion is difficult to control the composition stably. On the other hand, in the method of controlling multi-element non-metallic inclusions, it is difficult to reduce the size and number of inclusions and to ensure ductility. Therefore, it is difficult to improve the drawability and the fatigue resistance after drawing.

Therefore, in Patent Document 6, the range of the total oxygen content is defined within a certain range, the amount and composition of non-viscous inclusions are controlled, the size and number of non-viscous inclusions are reduced, and ductility is ensured. Thus, the distribution of the amount and size of the non-viscous inclusions is made preferable, and the inclusion composition is added to SiO ₂ and MnO, and selectively contains Al ₂ O ₃ , MgO, CaO, and TiO _2. The high-carbon steel wire rod is remarkably excellent in wire drawing and fatigue resistance after wire drawing by modifying the inclusion into multi-component oxide inclusions.

Further, Patent Document 7 discloses a method of defining the size of hard high SiO ₂ inclusions and reducing the amount of expensive deoxidizing alloy used.

  In addition, in order to control nonmetallic inclusions to have a lower melting point and can be easily stretched, several methods using an alkali metal compound have been proposed. Patent Document 8 proposes a method of controlling the amount of alkali metal compound in non-metallic inclusions to 4 to 24% and improving stretchability by using a mixture of a Si-based deoxidizer and an alkali metal compound. Yes.

Furthermore, in Patent Document 9, the Al ₂ O ₃ —CaO—SiO ₂ —MgO—MnO-based low melting point inclusion contains 0.5 to 10% of an alkali metal oxide and has excellent fatigue strength. Si deoxidized steel has been proposed.

Furthermore, Patent Document 10, 11, _LiO 2 to the low-melting _inclusions, Na 2 O, at least one of _{K 2} O, in a total amount of _{LiO 2, Na 2 O, K} 2 O 0.5~20 A steel wire for highly clean springs having excellent fatigue characteristics, characterized by containing the element%, is disclosed. Among these, LiO ₂ , Na ₂ O, and K ₂ O are not equivalent, and an appropriate amount of LiO ₂ , Na ₂ O, and K ₂ O is added to the oxide inclusions by positively adding Li, which has a particularly strong deoxidizing power, as the origin of oxide inclusions. It is described that the effect is enhanced when LiO ₂ is contained.

Japanese Patent Publication No.57-22969 Japanese Patent Laid-Open No. 55-24961 Japanese Patent Publication No.54-7252 JP 50-81907 A Japanese Patent Publication No.57-35243 Japanese Patent Publication No. 4-8499 Japanese Patent No. 3294245 Japanese Patent No. 2654099 Japanese Patent No. 3719131 Japanese Patent Laying-Open No. 2005-29888 Japanese Patent No. 4315825

690th edition of the Iron and Steel Institute of Japan, “Steel Handbook II Steelmaking and Steelmaking”, page 690

  As described above, high carbon steel wires having high wire drawing performance have been supplied by ensuring the cleanliness of molten steel, softening nonmetallic inclusions, preventing Al contamination, and the like.

  However, in recent years, in the wire drawing process, the improvement of productivity by omitting patenting after the primary drawing has been directed, and the market for saw wires that are finer than steel cords for automobile tires has been expanded. The inclusion size in the wire that causes disconnection is much smaller than the conventional (20 μm or more), and the inclusions are not sufficiently stretched only by the conventional inclusion softening technique, making it difficult to cope with them.

  The present invention has been made in view of the above circumstances, and based on the multi-component control technology for oxide-based non-metallic inclusions, by utilizing a compound other than oxides, the melting point of the non-metallic inclusions In addition, by reducing the inclusions after rolling the wire rods, it is possible to respond to strict applications, the disconnection rate during wire drawing is extremely low, and the fatigue properties after wire drawing are excellent. The issue is to supply high-performance, high-carbon wires.

  The present inventors conducted a detailed investigation on the relationship between the composition of nonmetallic inclusions and the melting point and viscosity. As a result, by allowing a multi-component inclusion to coexist with an alkali metal such as Na and a small amount of fluorine, the melting point and viscosity of the inclusion can be further reduced, and the formation of a crystal phase can be suppressed, As a result, it has been found that inclusions after wire rod rolling can be refined.

  Furthermore, the present inventors have found that NaF molecules also have the effect of delaying the formation of the crystalline phase of nonmetallic inclusions.

  The present invention has been made based on the above findings, and the gist thereof is as follows.

(1) By mass%, C: 0.5 to 1.2%, Si: 0.15 to 2.5%, Mn: 0.20 to 0.9%, P ≦ 0.025%, S: 0 0.004 to 0.025%, Al: 0.000005 to 0.002%, Ca: 0.00001 to 0.002%, Mg: 0.00001 to 0.001%, Na: 0.000005 to 0.001 %, F: 0.000003 to 0.001%, the total oxygen content is 16 to 30 ppm, and the balance is a high carbon steel wire made of Fe and inevitable impurities, and is seen in the cross section in the wire L direction. Among oxide-based non-metallic inclusions (hereinafter referred to as “size inclusions”) having a minor axis of 0.5 μm or more, a major axis of 1.0 μm or more, and an equivalent circle diameter (surface equivalent diameter) of 1 μm or more, (% SiO ₂ ) = 40~95%, (% CaO) = 0.5~30%, (% Al 2 O 3) = 0. -30%, (% MgO) = 0.5-20%, (% MnO) = 0.5-10%, (% Na) = 0.2-7%, (% F) = 0. The ratio of the number of inclusions satisfying 17 to 8% (hereinafter referred to as “composition subject inclusions”), the number of inclusions subject to composition / the number of inclusions subject to size × 100 is 80% or more, High carbon steel wire rod with excellent fatigue characteristics after wire.

Here, (% SiO ₂ ), (% CaO), (% Al ₂ O ₃ ), (% MgO), (% MnO), (% Na), and (% F) are the SiO in the inclusions, respectively. ₂ , CaO, Al ₂ O ₃ , MgO, MnO, Na, F content (% by mass). (Same in the following)

  (2) Further, REM: 0.000005 to 0.001% is contained, and the inclusions to be composed are in an average concentration, and (% T. REM) = 0.3 to 1.0%, (% S ) = 0.05 to 0.2%, The high carbon steel wire rod having excellent wire drawing property and fatigue property after wire drawing according to the above (1).

  Here, (% T. REM) and (% S) are the total of rare earth elements in the inclusion and the S content (mass%), respectively. (Same in the following)

  (3) The high carbon steel wire excellent in wire drawing property and fatigue property after wire drawing according to (1) or (2), further comprising B: 0.0005 to 0.002%.

  (4) Further, Cr: 0.05-1.0%, Ni: 0.05-1.0%, Cu: 0.05-1.0%, Ti: 0.001-0.25%, Nb: It contains 0.001 to 0.25%, V: 0.001 to 0.25%, Mo: 0.05 to 1.0%, Co: 0.1 to 2%, or one or more. A high carbon steel wire excellent in the drawability and fatigue characteristics after drawing as defined in any one of (1) to (3).

  According to the present invention, inclusions after wire rod rolling can be miniaturized, can be used for strict applications such as saw wire, the disconnection rate at the time of wire drawing is extremely low, and the fatigue properties after wire drawing are also excellent. A highly functional high carbon wire can be obtained.

  Hereinafter, the present invention will be described in detail. First, the details of the mechanism of the present invention will be described. Unless otherwise specified, hereinafter, “%” means “mass%”.

  Conventional multi-component control technology for non-metallic inclusions is a technique for reducing the melting point and viscosity of silicate inclusions. In this silicate inclusion, Na and F have extremely strong affinity. From a microscopic viewpoint, Na ions and F ions are located adjacent to each other and affect the melting point and viscosity of silicate inclusions as NaF molecules.

The NaF-containing oxide starts to melt at a temperature of 1200 ° C. or lower, whereas the Na ₂ O single-added oxide or F (for example, CaF ₂ ) single-added oxide does not start to melt unless the temperature is higher than 1200 ° C. That is, by making Na and F coexist, an extremely low melting point can be realized.

  The melting point of 1200 ° C. or lower is close to the wire rolling temperature (1000 to 1200 ° C.) as well as the block rolling (1150 to 1300 ° C.) in the breakdown process of the continuously cast slab. Conventionally, it has been considered that stretching during the rolling of inclusions mainly occurs in the block rolling process. However, when Na and F coexist in the inclusions, the inclusions are stretched not only in the split rolling process but also in the wire rod rolling process. Therefore, inclusions can be remarkably refined by coexisting Na and F.

  In non-metallic inclusions, there is a potential to generate various crystal phases depending on the composition, but when a crystal phase is actually generated and grows greatly, it becomes a starting point for disconnection or the like. On the other hand, the addition of NaF molecules has the effect of remarkably delaying the formation of the crystal phase in addition to the effects of lowering the melting point and lowering the viscosity. As a result, since the starting point of disconnection or the like decreases, the disconnection rate at the time of wire drawing becomes extremely low.

  In addition, the effect with respect to inclusion stretchability of Na and F depends on the calculated amount of NaF in the inclusion, and the stretchability improves as the calculated amount of NaF increases. Here, the calculated amount of NaF refers to the mass% of NaF in the inclusions when Na and F are combined at a molar ratio of 1: 1.

  When the balance between Na and F is poor and excess Na or F is present, there is little effect on inclusion stretchability. For this reason, it is preferable to add (% Na) and (% F) so that the molar ratio is 1: 1, that is, the mass ratio is 1: 0.83.

  Patent Documents 8 to 11 disclose a method of utilizing an alkali metal oxide typified by Na. However, none of the documents mentions the necessity of coexistence of Na and F on the basis of silicate-based multi-component inclusions. That is, the technical ideas of the inventions of these documents are different from those of the present invention.

  Next, the reason for determining the content of each oxide constituting the oxide inclusion in the present invention will be described.

  First, the reasons for limiting the total amount of oxygen in steel will be described. Since the amount of non-metallic inclusions is increased in a wire material having a total oxygen amount exceeding 30 ppm, and the work material used for strict applications is not sufficient to avoid disconnection, the upper limit is set to 30 ppm. On the other hand, if a strong deoxidizing material such as Al or Mg is used in a large amount, it is easy to achieve a total oxygen amount of less than 16 ppm, but in order to control the composition of nonmetallic inclusions in the wire of the present invention. Requires 16 ppm or more total oxygen. When the total oxygen amount is less than 16 ppm or more than 30 ppm, the die life is extremely deteriorated. A more preferable range of the total oxygen amount is 17 to 25 ppm.

  Next, control of the composition and form of nonmetallic inclusions in the present invention will be described.

The steel wire rod of the present invention is an oxide-based non-metallic intervening having a minor axis of 0.5 μm or more, a major axis of 1.0 μm or more, and an equivalent circle diameter (surface equivalent diameter) of 1 μm or more as seen in a cross section in the wire L direction (length direction). (% SiO ₂ ) = 40 to 95%, (% CaO) = 0.5 to 30%, (% Al ₂ O ₃ ) = 0.5 to 30%, (% MgO) = 0.5-20%, (% MnO) = 0.5-10%, (% Na) = 0.2-7%, (% F) = 0.17-8% Inclusions (inclusions for composition) are 80% or more in number ratio (number of inclusions for composition / number of inclusions for size × 100).

  In the cross section of the wire L, inclusions having a minor axis of less than 0.5 μm are inclusions that are originally small in size or easily deformed during rolling. Inclusions having a major axis of less than 1.0 μm and an equivalent circle diameter of less than 1.0 μm are inclusions having a small original size. These inclusions are unlikely to cause deterioration of wire drawability and fatigue characteristics.

  Therefore, in the present invention, an oxide-based nonmetallic inclusion having a minor axis of 0.5 μm or more, a major axis of 1.0 μm or more, and an equivalent circle diameter of 1 μm or more, as seen in the cross section in the wire L direction, is an inclusion to be evaluated. It was called “target inclusion”.

  Next, the reason for limiting the composition range of inclusions to be composed will be described.

In order to soften and refine the non-metallic inclusions which is the object of the present invention, first, a combination of oxide compositions in a multi-component system is required. The basis of the oxide composition is a ternary system of SiO ₂ —CaO—Al ₂ O ₃ —MgO—MnO, and only by containing Na and F at the same time can softening and refinement of nonmetallic inclusions. The effect is demonstrated.

SiO ₂ is an important oxide that forms the basis of silicate inclusions. If (% SiO ₂ ) is less than 40%, the base multi-component inclusion itself does not become a silicate inclusion, and the effect of the present invention cannot be exhibited. When (% SiO ₂ ) exceeds 95%, it is no longer a multi-component inclusion, and quality deterioration due to large-sized SiO ₂ occurs.

  (% CaO) needs to be 0.5% or more in order to obtain the effect of lowering the melting point and viscosity due to the inclusion of multi-component inclusions. When (% CaO) exceeds 30%, CaO-rich hard inclusions are produced, resulting in deterioration of quality.

Al ₂ O ₃ contributes to softening of inclusions if it is in an appropriate amount, but if it exceeds 30% in (% Al ₂ O ₃ ), hard Al ₂ O ₃ inclusions are generated and the quality is greatly deteriorated. . If (% Al ₂ O ₃ ) is less than 0.5%, the effect of multi-component inclusions cannot be obtained.

(% MgO) needs to be 0.5% or more in order to obtain the effect of lowering the melting point and viscosity due to multi-component inclusions. When (% MgO) exceeds 20%, harmful inclusions such as olivine or forstenite (2MgO.SiO ₂ ) are generated.

(% MnO) needs to be 0.5% or more in order to obtain the effect of lowering the melting point and viscosity due to the multi-component inclusions. When (% MnO) exceeds 10%, it becomes not silicate inclusion but spessite (SiO ₂ —MnO—Al ₂ O ₃ ) inclusion, and the effect of addition of Na and F cannot be exhibited.

  Na and F are extremely important components in the present invention. If (% Na) is less than 0.2%, there is no effect of improving inclusion stretchability. On the other hand, when (% Na) exceeds 7%, the effect is saturated, and problems such as a sudden increase in the amount of dust generated when Na is added occur. Preferably it is less than 4%.

  Moreover, when (% F) is less than 0.17%, there is no improvement effect of inclusion stretchability. When (% F) exceeds 8%, the effect is saturated and the harmful effect such as a rapid increase in the amount of refractory melt is increased. As described above, Na and F become NaF molecules in the inclusions and exert their effects. Therefore, the molar ratio of Na and F in the nonmetallic inclusions is 1: 1, that is, by mass ratio ( % Na): (% F) is preferably added so as to be close to 1: 0.83.

  In addition, when counting oxide-based non-metallic inclusions (inclusions for size) having a minor axis of 0.5 μm or more, a major axis of 1.0 μm or more, and an equivalent circle diameter of 1 μm or more, as seen in the wire cross section, the inclusion of the size target It is necessary that the number ratio of inclusions (composition subject inclusions) satisfying the above composition (number of inclusions intended for composition / number of inclusions targeted for size × 100) is 80% or more.

When the number ratio is less than 80%, it means that the effect of extending the inclusions by Na + F is not enjoyed. Further, below 80% means, for example, that there is a certain amount of interposition of a composition that does not belong to multi-component inclusions such as MgO-based and Al ₂ O _3- based hard inclusions. , Wireability, and fatigue properties after wire drawing are impaired.

  The reason for defining the size of the inclusion is to count only inclusions of a size that deteriorates the drawability and fatigue characteristics.

  In the present invention, both Na and F are added to the steel, both Na and F are contained in the silicate-based multi-component oxide inclusions, and the composition of the inclusions is controlled. In addition, fatigue characteristics after wire drawing can be ensured. Recently, the use for drawing a steel wire to a smaller diameter is increasing, and in such a use, the high carbon steel wire of the present invention exhibits particularly excellent performance.

Na and F may be added as a NaF compound, or Na and F may be added separately (for example, Na ₂ CO ₃ and CaF ₂ ).

When F is added at the same time as metal Si, SiF ₄ is generated and gasified, and the yield of F deteriorates.

  By controlling (% T. REM) (total content of rare earth elements such as La, Ce, and Nd) and (% S) in the non-metallic inclusions, the drawability can be further improved. The reason for this is as follows.

REM (La, Ce, Nd, etc.) has a strong affinity for S and is incorporated into multi-component inclusions while fixing S in the form of REM oxysulfide (REM ₂ O ₂ S). Thereby, the amount of solid solution S in steel can be reduced and precipitation of MnS is suppressed. MnS precipitated in steel may be a starting point for wire breakage during wire drawing, and by suppressing this precipitation, wire drawability and fatigue properties after wire drawing are improved.

  It is preferable to control the inclusion (% T. REM) in the range of 0.3 to 1.0% and (% S) in the range of 0.05 to 0.2%. If (% T.REM) is less than 0.3%, the S-fixing ability is insufficient, and if it exceeds 1.0%, the REM oxide concentration in the non-metallic inclusions increases and the stretchability is sufficiently improved. May not. Also, if (% S) is less than 0.05%, the amount of S fixation is too small to be effective, and if it exceeds 0.2%, CaS or the like is generated in non-metallic inclusions, and the stretchability is sufficiently improved. May not.

  In addition, the frequency of disconnection starting from MnS is less than that of disconnection starting from oxide-based nonmetallic inclusions. Therefore, it is first necessary to properly control the composition of oxide-based nonmetallic inclusions in steel.

  Next, the definition of the component composition of the steel of the present invention will be described. So-called killed steel is used for the JISG3502 piano wire, the JISG3506 hard steel wire, and the JISG3561 oil temper wire for valve springs used as high carbon steel wires. In view of this JIS standard, ease of manufacture, and practical use, the present invention defines the component ranges as follows.

  That is, in mass%, C: 0.5 to 1.2%, Si: 0.15 to 2.5%, Mn: 0.20 to 0.9%, P ≦ 0.025%, S: 0.00. 004 to 0.025%, Al: 0.000005 to 0.002%, Ca: 0.00001 to 0.002%, Mg: 0.00001 to 0.001%, Na: 0.000005 to 0.001% F: 0.000003 to 0.001%, Cr: 0.05 to 1.0%, Ni: 0.05 to 1.0%, Cu: 0.05 to 1.0, as necessary %, Ti: 0.001 to 0.25%, V: 0.001 to 0.25%, Nb: 0.001 to 0.25%, Mo: 0.05 to 1.0%, Co: 0.0. It is steel containing 1-2% of 1 type or 2 types or more.

  Moreover, the effect of this invention will become large when REM: 0.000005-0.001% is contained. Furthermore, when B: 0.0005 to 0.002% is added, steel excellent in wire drawing properties and fatigue properties after wire drawing can be obtained.

  C is an element that is economical and effective in strengthening steel. In order to obtain the strength required as a hard steel wire, 0.5% or more is required. However, if it exceeds 1.2%, the ductility of the steel decreases and becomes brittle, and secondary processing becomes difficult. A more preferable concentration of C is 0.51 to 1.1%.

  Si and Mn are necessary for deoxidation and inclusion composition control. When Si is less than 0.15% and Mn is less than 0.20%, there is no effect. It is also effective as a steel strengthening element. However, when Si exceeds 2.5% and Mn exceeds 0.9%, the steel becomes brittle. More preferable ranges of Si and Mn are 0.16 to 2.3% and 0.25 to 0.85%, respectively.

  P deteriorates wire drawing workability in high carbon steel, and further deteriorates ductility after wire drawing. Therefore, the P content needs to be 0.025% or less, and more preferably 0.020% or less.

  S also deteriorates the wire drawing workability and further deteriorates the ductility after the wire drawing. On the other hand, in order to secure the descaling property of the steel material, it is necessary to secure the S concentration to some extent. Therefore, the concentration of S is 0.004 to 0.025%, preferably 0.005 to 0.020%.

  Al is an element that affects the inclusion composition of the present invention, and a predetermined inclusion composition cannot be obtained if it is too much or too little. Therefore, the Al concentration is set to 0.000005 to 0.002%, preferably 0.0002 to 0.001%.

  Ca is also an element that affects the inclusion composition of the present invention, and a predetermined inclusion composition cannot be obtained if it is too much or too little. Therefore, the Ca concentration is set to 0.00001 to 0.002%, preferably 0.000013 to 0.0015%.

  Mg is an element that affects the inclusion composition of the present invention, and a predetermined inclusion composition cannot be obtained if it is too much or too little. Therefore, the Mg concentration is 0.00001 to 0.001%, preferably 0.000011 to 00008%.

  Na and F are extremely important components in the inclusion composition of the present invention, and the Na and F concentrations in the steel affect the inclusion composition.

  Na is an element that affects the inclusion composition of the present invention, and a predetermined inclusion composition cannot be obtained if it is too much or too little. Therefore, the concentration of Na is set to 0.000005 to 0.001%, preferably 0.000007 to 0.0005%.

  F is also an element that affects the inclusion composition of the present invention, and a predetermined inclusion composition cannot be obtained if it is too much or too little. Therefore, the concentration of F is set to 0.000003 to 0.001%, preferably 0.000005 to 0.0005%.

  The steel of the present invention preferably contains the following components.

  Cr has the effect of making the pearlite lamella fine and increasing the strength of the steel. The amount necessary to obtain this effect is 0.05%, and addition beyond that is preferable. However, if added over 1.0%, the ductility is inhibited, so the upper limit is made 1.0%.

  Ni strengthens steel by the same effect as Cr. In order to obtain the effect, addition of 0.05% or more is preferable. If the addition exceeds 1.0%, the ductility decreases, so the upper limit is made 1.0% or less.

  Cu has the effect of improving the scale characteristics and corrosion fatigue characteristics of the wire. In order to obtain the effect, addition of 0.05% or more is preferable. If the addition exceeds 1.0%, the ductility decreases, so the upper limit is made 1.0% or less.

  Ti, Nb, and V have the effect of increasing the strength of the wire by precipitation strengthening. In any case, if it is less than 0.001%, there is no effect, and if it exceeds 0.25%, precipitation embrittlement is caused. Therefore, the content is made 0.001 to 0.25%. It is also effective to add these elements to reduce the γ grain size during patenting.

  Mo is an element that improves the hardenability of steel. In the case of the present invention, the addition of the steel can increase the strength of the steel, but the addition of an excessive amount makes the steel excessively hardened and makes it difficult to work. Therefore, the Mo addition range is 0.05 to 1.0%.

  When Co is contained in an amount of 0.1 to 2%, ductility is improved due to the effect of suppressing the formation of proeutectoid cementite of the hypereutectoid steel.

B improves the hardenability of the steel and, when present in the austenite in a solid solution state, concentrates at the grain boundary to suppress the formation of non-pearlite precipitates such as ferrite, pseudo pearlite, and bainite, and improves the drawability. Let If the addition amount is too small, this effect cannot be obtained, so the lower limit is made 0.0005%. On the other hand, if added too much, precipitation of coarse Fe ₃ (CB) ₆ carbide in austenite is promoted, and the wire drawing property is adversely affected. Therefore, the upper limit is made 0.002%.

  REM is an element that affects the inclusion composition of the present invention. If the amount of REM is too much or too little, a predetermined inclusion composition for further improving the drawability cannot be obtained, so the content is made 0.000005 to 0.001%.

  Next, the manufacturing method of the high carbon steel wire of this invention is demonstrated.

  The steel of the present invention can be smelted by simple ladle refining after the molten steel that has undergone refining in a converter or electric furnace is taken out into a ladle. As simple ladle refining, CAB (capped argon bubbling), SAB (shielded argon bubbling), and CAS (component adjustment by SAB) described in Non-Patent Document 1 can be used.

  In order to reduce the total amount of oxygen in the steel to 30 ppm or less, the mixing time of the converter slag flowing out from the converter to the ladle at the time of steel output is suppressed as much as possible, and the sedation time of the simple ladle refining (after It is effective to secure the time until continuous casting is started for about 20 to 40 minutes and promote the floating separation of the oxide. It is also effective to prevent air oxidation of the molten steel between the ladle and the tundish, and between the tundish and the continuous casting mold.

  On the other hand, in order to make the total oxygen amount in the steel 16 ppm or more, the strong deoxidizing element Al or Mg is not added to the steel as much as possible, and Ti is kept to the minimum addition and a simple ladle. This can be realized by not performing the refining process for a long time.

  Specifically, it is set to about 25 to 40 minutes by melting synthetic slag and stirring with molten steel, secondary deoxidation, fine component adjustment, molten steel temperature adjustment, and argon bubbling in the pan. And by argon bubbling in the pan, uniform mixing of components and coolant and floating separation of inclusions are attempted.

  Performing full-scale ladle refining such as vacuum degassing is not preferable because there is a high possibility that the total amount of oxygen in the steel will be less than 16 ppm.

In order to make inclusions whose size ratio in steel is (% Al ₂ O ₃ ) 30% or less 80% or more in terms of the number ratio, it is necessary to prevent Al from being mixed into the steel. Of course, it is preferable not to use Al as a deoxidizing agent, but to use Fe-Si and Si-Mn as alloy irons added at the time of steelmaking, which also have low Al content.

For example, normal Fe-Si contains about 1.5% Al, but low Al-Fe-Si with an Al content of about 0.01 to 0.10% is preferably used. it can. In addition, using a refractory having a low alumina content as the ladle refractory is also effective in increasing the number ratio of inclusions having (% Al ₂ O ₃ ) of 30% or less to 80% or more.

In addition, since there is always some Al contamination from Al in the alloy iron added to the steel or alumina in the ladle or tundish refractory, inclusions in which (% Al ₂ O ₃ ) is 0.5% or more Can be 80% or more in terms of the number ratio.

In the inclusions (% CaO), (% SiO 2) may, CaO slag components on the pot in the simple ladle refining, as well as adjust the SiO ₂ content, 30 ppm or less total oxygen content in the above-described steels and By adopting the manufacturing conditions for doing so, it can be within the scope of the present invention.

Specifically, the basicity (CaO / SiO ₂ mass ratio) of the slag on the pan is adjusted by adjusting the components and amount of the SiO ₂ —CaO-based synthetic slag added to the ladle. The basicity of the pan slag is preferably 0.9 to 1.3. Further, by adopting the production conditions in which the total amount of oxygen in the steel is 30 ppm or less, it is possible to prevent an increase in inclusion (% SiO ₂ ) due to oxidation of the Si component in the steel. it can.

  In addition, about the point which makes (% MgO) of inclusions 0.5-20% and (% MnO) 0.5-10%, it mixes from the MgO source in a refractory, oxidation of Mn in steel Based on the above, it can be made within the scope of the present invention by ordinary steel melting.

  About the point made into (% Na) = 0.2-7% of inclusions, and (% F) = 0.17-8%, as above-mentioned, by adding together Na and F in steel, it intervenes. Both Na and F can be included in the product within the scope of the present invention.

At this time, Na and F may be added as a NaF compound, or Na and F may be added separately (for example, Na ₂ CO ₃ and CaF ₂ etc.). When F is added at the same time as metal Si, SiF ₄ is generated and gasified, and the yield of F deteriorates.

  In order to make (% T.REM) in the inclusions 0.3 to 1.0% and (% S) 0.05 to 0.2%, REM is added to the steel by an amount corresponding to several ppm. Good. The REM added to the steel reacts with S in the steel to form REM oxysulfide and coalesces with the silicate inclusions. As a result, it is possible to contain (% T.REM) = 0.3 to 1.0% and (% S) = 0.05 to 0.2% in average concentration in the inclusions to be composed.

  The melting in this example was performed by an LD converter. When steel was taken out from the LD converter into the ladle, a so-called dart-type converter slag closing jig was used to keep the slag out of a small amount (less than 50 mm thickness).

  In addition, a carburizing material for adjusting the components of C, Si, and Mn, and deoxidized alloy iron such as Fe—Si, Fe—Mn, and Si—Mn were added during steel output. As the deoxidized alloy iron, one containing as little a strong deoxidizing element as Al and Mg as possible was used. In addition, argon was blown from the bottom of the ladle during or after steel output.

The molten steel in the ladle after receiving steel is so-called killed steel deoxidized by Si, Mn, or the like. After moving the ladle molten steel refining implementation position, after the addition of synthetic slag of SiO ₂ -CaO based in pan, preparative performed included argon blowing stirring molten steel in the pan than the bottom of the pan, the CAB simplified ladle refining went.

Next, the secondary deoxidizer was added to the molten steel as alloy iron. The secondary deoxidizing material contains metals Ca, Al, Mg, Si, and the like. As needed, Na, F, and REM were added in the molten steel in a pan. NaF was added when both Na and F were added, Na ₂ CO ₃ was added when Na was added alone, and CaF ₂ was added when F was added alone. When F was added, it was added at a timing different from the addition of the alloy containing Si and the secondary deoxidizer.

  After adding the second deoxidizing material, the components were further finely adjusted to complete the ladle molten steel refining. After finishing the ladle molten steel refining, continuous casting was performed after securing a suitable sedation time (about 20 to 40 minutes) so that the total oxygen content in the steel was 16 to 30 ppm. Molten steel is continuously cast from the ladle via the tundish. At that time, in order to suppress air oxidation between the ladle and the tundish and in the tundish as much as possible, sealing with an inert gas was performed. . The obtained slab was subjected to slab heating furnace bundling, slab rolling, and slab refining, and then a 5.5 mmφ wire was manufactured by wire rolling through the heating furnace.

  In order to investigate the number and composition of non-metallic inclusions, a sample with a length of 0.5 m was cut out from one coil of a 5.5 mmφ wire rod, and a small sample with a length of 11 mm from any 10 locations in the L direction (length direction). Samples were cut out and each was examined by examining the entire longitudinal section passing through the center line in the length direction. The number and composition of non-metallic inclusions is an oxide-based non-metallic inclusion having a minor axis of 0.5 μm or more, a major axis of 1.0 μm or more, and a circle equivalent diameter of 1 μm or more, and the composition of each inclusion. Analyzed by X-ray spectroscopy.

  Among the inclusions targeted for size, those included in the composition range of the present invention were defined as inclusions intended for composition, and the number ratio (number of inclusions intended for composition / number of inclusions targeted for size × 100) was evaluated. In addition, the average composition of all inclusions to be sized was also calculated. However, for REM and S, the average composition of inclusions intended for composition was calculated.

  Thereafter, the 5.5 mmφ wire was drawn to 0.175 mmφ or less, and the wire drawing characteristics and the die life were investigated. For the wire drawing characteristics, the disconnection frequency with respect to a constant drawing dose was defined as a disconnection index, and a disconnection index of 5 or less was considered good. The die life was evaluated as an index that becomes 100 as the minimum allowable life of the current process material and becomes larger as the life becomes longer. A die life index of 100 or more is good.

  Furthermore, in order to evaluate the fatigue characteristics, a rotational fatigue test was performed on the wire drawn to 0.175 mmφ. In the rotation fatigue test, the stress was changed in various ways and the number of repetitions until fracture occurred was investigated. The stress that was cut at the number of repetitions of 100,000 was corrected with the coefficient of tension in the mechanical test, and was evaluated as a stress index.

  Tables 1 to 4 show the results of the invention examples and comparative examples. Numerical values that fall outside the scope of the present invention are underlined.

  Invention Example No. For 1 to 24, good results were obtained. No. 8 to 18 are levels in which REM is added in addition to Na and F. In this case, the die life and fatigue characteristics are improved. Furthermore, no. Nos. 19 to 24 are levels obtained by adding B to steel, and further improvement in die life and fatigue characteristics was confirmed.

  Next, the result of the comparative example will be described. No. No. 25, when Na and F were not added, No. 26 shows no. 27 is a case where only F is added alone. In both cases, the inclusion number ratio (the number of inclusions to be composition / the number of inclusions to be sized × 100, hereinafter referred to as “inclusion number ratio”) is zero. It is worse than that.

  No. No. 28 is the case where the total oxygen amount was higher than the range of the present invention because the sealing in the tundish was insufficient. The number of inclusions was large, and the die life and fatigue characteristics deteriorated.

No. 29 to 32 are levels at which the inclusion number ratio is less than 80%. No. No. 29 used a refractory having a high content of Al ₂ O ₃ or MgO, and therefore there are many inclusions of Al ₂ O ₃ and MgO that are considered to be caused by the refractory in the inclusions. As a result, the inclusion number ratio was lower, and the disconnection index, die life, and fatigue characteristics deteriorated.

No. No. 30 is because the composition ratio of the SiO ₂ —CaO-based synthetic slag has changed (% SiO ₂ ) in the non-metallic inclusions, so that the number ratio of inclusions is lower and the inclusions are partly hard Appeared, and the disconnection index, die life, and fatigue characteristics deteriorated slightly.

No. No. 31 had a slightly larger LD slag outflow, coarse inclusions of SiO ₂ alone appeared in the deoxidation process, and (% SiO ₂ ) in non-metallic inclusions increased. As a result, the inclusion number ratio was lower, and the disconnection index and fatigue characteristics deteriorated.

No. No. 32 used normal alloy iron with a high Al concentration instead of low Al alloy iron as a deoxidizing alloy, and (% Al ₂ O ₃ ) in nonmetallic inclusions increased. As a result, the inclusion number ratio was lower and a large number of hard Al ₂ O ₃ inclusions were produced, and the disconnection index, die life, and fatigue characteristics were very poor.

  No. No. 33 had a high S concentration in the steel, and (% S) in the nonmetallic inclusions was higher than the range of the present invention, and the disconnection index, die life, and fatigue characteristics deteriorated.

  No. Since REM added too much REM, (% T.REM) in a nonmetallic inclusion became a value higher than the range of this invention, and the disconnection index | exponent, die | dye life, and fatigue characteristics deteriorated.

Claims (5)

% By mass
C: 0.5 to 1.2%
Si: 0.15-2.5%,
Mn: 0.20 to 0.9%,
P ≦ 0.025%,
S: 0.004 to 0.025%,
Al: 0.000005 to 0.002%,
Ca: 0.00001 to 0.002%,
Mg: 0.00001 to 0.001%,
Na: 0.000005 to 0.001%,
F: 0.000003 to 0.001%
Is a high carbon steel wire consisting of 16 to 30 ppm in total oxygen, the balance being Fe and inevitable impurities,
Oxide-based non-metallic inclusions (hereinafter referred to as “size inclusions”) having a minor axis of 0.5 μm or more, a major axis of 1.0 μm or more, and an equivalent circle diameter (surface equivalent diameter) of 1 μm or more as seen in the cross section in the wire L direction. Of these, (% SiO ₂ ) = 40 to 95%, (% CaO) = 0.5 to ₃₀ %, (% Al ₂ O ₃ ) = 0.5 to 30%, (% MgO) = 0.5 to 20 %, (% MnO) = 0.5 to 10%, and (% Na) = 0.2 to 7% and (% F) = 0.17 to 8% The ratio of the number of inclusions), the number of inclusions for composition / the number of inclusions for size × 100 is 80% or more, and a high carbon steel wire rod excellent in wire drawing and fatigue properties after wire drawing.
Here, (% SiO ₂ ), (% CaO), (% Al ₂ O ₃ ), (% MgO), (% MnO), (% Na), and (% F) are the SiO in the inclusions, respectively. ₂ , CaO, Al ₂ O ₃ , MgO, MnO, Na, F content (% by mass). Furthermore, REM: 0.000005 to 0.001%
That the inclusions to be composed satisfy the (% T. REM) = 0.3 to 1.0% and (% S) = 0.05 to 0.2% at an average concentration. The high carbon steel wire excellent in wire drawing property and fatigue property after wire drawing according to claim 1.
Here, (% T. REM) and (% S) are the total of rare earth elements in the inclusion and the S content (mass%), respectively. Furthermore, B: 0.0005 to 0.002%
The high carbon steel wire excellent in wire drawing property and fatigue property after wire drawing according to claim 1 or 2. Furthermore, Cr: 0.05 to 1.0%,
Ni: 0.05 to 1.0%,
Cu: 0.05 to 1.0%,
Ti: 0.001 to 0.25%,
Nb: 0.001 to 0.25%,
V: 0.001 to 0.25%,
Mo: 0.05-1.0%,
Co: 0.1 to 2%
1 or 2 types or more of these are included, The high carbon steel wire rod excellent in the wire drawing property and the fatigue characteristic after wire drawing of Claim 1 or 2 characterized by the above-mentioned. Furthermore, Cr: 0.05 to 1.0%,
Ni: 0.05 to 1.0%,
Cu: 0.05 to 1.0%,
Ti: 0.001 to 0.25%,
Nb: 0.001 to 0.25%,
V: 0.001 to 0.25%,
Mo: 0.05-1.0%,
Co: 0.1 to 2%
The high carbon steel wire rod excellent in the wire drawing property and the fatigue property after wire drawing according to claim 3, comprising one or more of the following.